The present invention relates to a nozzle head for use in an ink jet printer.
A nozzle head having the features specified hereinbelow is disclosed in EP-A-0 402 172. This nozzle head comprises a channel plate defining a linear array of equidistant nozzles and a plurality of parallel ink channels, each connected to a respective one of the nozzles. On one side of the channel plate there is disposed an array of elongate fingers projecting towards the nozzle plate and extending in parallel with the ink channels. The ends of these fingers facing away from the channel plate are interconnected by a plate-like backing member which is formed integrally with the fingers. The fingers and the backing plate are made of a piezoelectric ceramic material. Every second finger is provided with electrodes and serves as an actuator which, when a print signal is applied to the electrodes, compresses the ink liquid contained in the associated ink channel, so that an ink droplet is expelled from the nozzle. The other fingers intervening between the actuators serve as support members which are rigidly connected to the channel plate so that they can absorb the reaction forces generated by the actuators.
Since a support member is provided between each pair of consecutive actuators, each actuator is substantially shielded against the reaction forces from its neighbors, so that undesired cross-talk between the various channels is reduced.
However, when one of the actuators is activated, e.g. expanded, the support members adjacent thereto on both sides are elastically deformed to some extent, so that the backing plate is slightly deflected. This effect becomes more significant when a plurality of neighboring actuators are activated simultaneously, whereby the stresses applied to the backing plate are accumulated. In this case the deformation of the backing plate will also affect the actuators which are disposed at a comparatively large distance from the active actuators and will cause the generation of parasitic acoustic waves in the ink channels where no droplets are to be expelled. Thus, there exists a problem which can be termed "long-range cross-talk."
It is an object of the present invention to provide a nozzle head in which long-range cross-talk can be suppressed more efficiently. According to the present invention, the array of fingers is divided into a number of separate blocks, and each block comprises only one support member and only one or two actuators.
As a result, the reaction forces of the actuator or actuators of one block are directly absorbed by the support member of the same block and are confined to this particular block, so that they will have substantially no effect on the other blocks. Thus, the undesired long-range cross-talk phenomenon is largely eliminated.
The use of not more than two actuators per block has the advantage that the spatial configuration of the actuators in relation to the support member and the borders of the block is the same for all actuators of the array, except for mirror symmetry in case of two actuators disposed on both sides of the support member. Thus, the subdivision of the array of fingers into separate blocks will not cause any differences in the performance of the actuators during the process of droplet generation.
In a preferred embodiment of the present invention, each block has two actuators disposed on either side of the support member. This has the advantage that the density with which the fingers (actuators and support members) are arranged in the direction of the linear nozzle array is only 3/2 of the density of the nozzles. As a result, when the density of the nozzles is reduced for enhancing the resolution of the print head, the pitch of the fingers remains comparatively large which facilitates the manufacture of the array of fingers.
In this embodiment, there may occur a certain amount of cross-talk between the two channels associated with the same block. However, since the number of different energizing patterns which have to be considered in this case is small, an electronic compensation of the cross-talk by appropriately controlling the voltages applied to the actuators is greatly facilitated. In fact, only two cases have to be taken into consideration, i.e. (a) the case in which only one of the two actuators is energized and (b) the case in which both actuators of the block are energized. For compensating the cross-talk in these two cases, it is therefore sufficient to provide two different sets of voltages to be applied to the two actuators.
The array of fingers may be additionally supported by a separate backing member disposed on the side of the array opposite to the channel plate and extending over all the blocks. This backing member should however have a comparatively high flexibility, so that the mechanical coupling between the various blocks is limited to a tolerable amount. More preferably, the backing member has an anisotropic rigidity, such that it is comparatively stiff in the direction parallel with the ink channels but is rather flexible in the direction transverse to the ink channels. This can be achieved for example by a grid-like backing member having a number of beams extending longitudinally of the ink channels and each being disposed over one of the blocks.